Evaluation of super-responders to cardiac resynchronization therapy in the presence of left bundle branch block and absence of scar in the posterolateral wall of the left ventricle

Patients with heart failure (HF) undergoing cardiac resynchronization therapy (CRT) who exhibit above-expected improvement are known as super-responders. We assessed the rate of super-responders in a population with left bundle branch block (LBBB) > 150 ms in the absence of scar tissue in the left ventricular posterolateral wall as well as prognostic variables. In this prospective observational cohort study (n=20) an electrocardiogram (ECG) was performed pre- and post-CRT. The classic and Strauss LBBB criteria were adopted (> 150 ms). The percent (%) reduction of the QRS was calculated after implantation. All patients responded to the Minnesota Living with Heart Failure questionnaire and underwent an echocardiogram to measure left ventricular ejection function (LVEF), left atrium (LA) diameter, left ventricular end-systolic volume (LVEDV), left ventricular end-diastolic volume (LVESV), and left ventricular end-diastolic diameter (LVEDD) pre- and 6 months post-CRT. Cardiac magnetic resonance imaging (MRI) measured the presence of scar tissue in the posterolateral LV wall and the total scar burden (% LV mass). Fisher's exact test and the Mann-Whitney test were performed to evaluate possible prognostic variables. The mean age was 58.20 +/- 8.79 years old, 60% female, with a mean LVEF of 28.15 +/- 5.10%, ECG with LBBB mean QRS of 162.15 +/- 7.86 ms, LBBB > 150 ms with Strauss standard in 90% of cases, and 90% with non-ischemic cardiomyopathy. Twelve cases (60%) of super-responders (reduction > 30% LVESV after 6 months) were observed. Super-responders did not present a difference in response in sex (12 vs 8 P=0.67), age (58.67 vs 57.7 P=087), Minnesota quality of life (55.50 vs 67.70 P=0.2), % initial QRS reduction (21.16 vs 18.69 P=0.21), LVEF (29.25 vs 26.5 P=0.38), LVEDD (66.33 vs 67.67 P=0.83), LVEDV (211.16 vs 228.53 P=0.75), LVESV (145.83 vs 167.00 P=0.75), or LA diameter (41.58 vs 43.63 P=0.45). The presence of LBBB > 150 ms, using the Strauss standard (90%) and the absence of scar in the posterolateral wall may account for these positive results. Super-responders benefit the most from CRT, and the results of this study can contribute to a better selection of CRT candidates.